The present invention relates to a pneumatic radial tire and manufacturing method of the same, and more particularly to a pneumatic radial tire which enables many kinds productions in small quantities to be efficiently performed and manufacturing method of the same.
Generally, a belt layer for a pneumatic radial tire is formed in a manner that a wide calendar material calendered to impregnate a number of reinforcing cords with unvulcanized rubber is bias-cut to a width of a belt, the reinforcing cords having been pulled out from a creel stand and aligned with one another, a number of cut pieces obtained by the bias-cutting are joined together for forming a long belt sheet material where the cut ends thereof are left and right edges, and then this long sheet material is wound on a drum and placed in temporary stock. A belt member for one tire is obtained by pulling out the belt sheet material from the drum during belt layer formation and cutting the sheet material to a length equal to a circumference of the belt layer in a direction along the reinforcing cords.
However, a belt member for one tire is different from another in width and length depending on a tire size. Thus, for forming belt members in the above manner, belt sheet materials different from one another must be stocked for respective tire specifications. For this reason, a great many kinds of belt members were stocked, which created a problem of requiring wide stock space. The impossibility of utilizing a belt member for the other tire specifications leads to such problems of leaving end portions of belt sheet materials for respective tire specifications as waste and requiring more operations during a tire manufacturing process. Moreover, for performing production of many kinds in small quantities, it was necessary to frequently carry out setup changing work for replacing a drum having taken up a long sheet material with another at each time when tire specifications were changed.
The object of the present invention is to solve the above described problems of stock space for belt members for respective tire specifications and material waste, and also is to provide a pneumatic radial tire which enables production of many kinds in small quantities to be efficiently performed and manufacturing method of the same.
In order to achieve the above described object, a pneumatic radial tire of the present invention has a belt layer disposed radially outer to a carcass layer in a tread section of the tire, the belt layer being formed of strip pieces each comprising a plurality of reinforcing cords and having a predetermined width, the strip pieces being arranged at a predetermined angle relative to the circumferential direction of the tire, one round portion of the belt layer in the circumferential direction of the tire comprising an integral number of the strip pieces juxtaposed in a manner such that each two adjacent strip pieces butts against each other along their longitudinal edges.
According to the present invention, the strip pieces are obtained by cutting a strip material having a predetermined width to a predetermined length at a predetermined angle.
In the pneumatic radial tire, if a length of the belt layer is L, a width of the strip pieces is A, an inclined angle of the strip pieces relative to the circumferential direction of the tire is xcex8 and the number of the strip pieces is N, the inclined angle xcex8 should preferably be set such that the number N of the strip pieces can be an integer in the following expression.
xcex8=sinxe2x88x921(Nxc3x97A/L)
The method manufacturing of a pneumatic radial tire of the present invention comprises the steps of feeding a strip material comprising a plurality of reinforcing cords and having a predetermined width from a standard measure feeding device which is adjustable in its feeding angle to a carrier conveyor, cutting said strip material to a predetermined size in sequence to form strip pieces while alternately moving the strip material and the carrier conveyor intermittently in synchronization with each other, transferring the strip pieces onto the carrier conveyor, forming a belt member having a length equal to a length L of a belt layer for one tire by butting the strip pieces against each other along their longitudinal edges, and using the belt member as the belt layer. In this case, if a width of the strip material is A and the number of the strip pieces for forming the belt layer is N, and an angle xcex8 for cutting the strip material to the predetermined size relative to the moving direction of the standard measure feeding device should be set such that the number N of the strip pieces can be an integer in the following expression.
xcex8=sinxe2x88x921(Nxc3x97A/L).
As described above, according to the present invention, a belt layer for one round of a tire is formed by inclining at a predetermined angle the integral number of predetermined width strip pieces, each of which is composed of a plurality of reinforcing cords, and by joining these strip pieces together in a manner such that two adjacent strip pieces butts against each other along their longitudinal edges. Thus, during belt layer formation, the predetermined width strip material is cut to a predetermined size in sequence at a predetermined inclined angle, the integral number of strip pieces obtained by cutting are butted against one another along their longitudinal edges and thereby the belt layer can be formed to have a length for one tire. Even if the size of a tire to be manufactured varies, since many sizes are dealt with by changing the cutting angles, the cutting lengths and the joined number of the strip pieces, various belt layers can be formed from the same strip material. As a result, efficient production of many kinds in small quantities can be performed. Therefore, the problem of requiring stock space for respective tire specifications as well as causing material waste can be eliminated. Moreover, large scale setup changing work will be unnecessary, thus enabling high efficiency manufacturings of many kinds of tires in small quantities.